Control system for alternating current motors



' March 2, 1943. E, SEEGER HAL 2,312,592

CONTROL SYSTEM FORALTERNATING CURRENT MOTORS Filed June 16, 1941 2 Sheets-Sheet l 1 2 3 b L L L z *1 1 '2 a .1 D (I) 2x 2 E O D Q. .4 Q 0 U YE \BB EH5! H OPEN 2 FORWARD 1 OPEN MOTOR A 02 B N MOTOQS A and B REVERSE v Mmh 2, 1943. Efw, SEE E ET AL 2,312,592

CONTROL SYSTEM FOR ALTERNATING CURRENT MOTORS Filed June 16, 1941 2 Sheets-Sheet 2 g b xfi z U L L :2 a 5 2 E 5 t OPEN CLOSE U Q Q 1 2. 3 4 5 6 l EHEIEHEIEHE] EH3 El-El ram/1.1205

Apm' -m J CLOSE TORQUE LBrKN. OPEN Patents 2 unis.

' i control I rd particularly ce of polyphase ialternating on the control oi duction motors.

In the conventional load speed substantial rotation oi the magnetic letter is dependent oi- 'l'll motor, the no the speed of the stator, which .3 on the oi poles and the frequency the source of current supply. When the motor is running loaded, its speed may be varied by the insertion of resistance in its primary or secondery circuit, but the re= sulting speed reduction of the motor depends upon the load, and its no-loed speed remains substantially the same, irrespective of the value or the resistance.

For certain applications it is desirable that the starting torque oi the motor, that the tordue at zero speed, be relatively low and that the torque reletively high normal speed, which opprocches the synchronous speed. At the time it is desirahle to change the speed-torque characteristic for given applications within very wide limits. It is further frequently desirable to employ simple electrical means for controlling the low loeci speed of induction motor drives, wi hout resorting to special generators efiording frequency and voltage control of the power supply.

Such a control is desirable, for instance, in motor drives for the chucks or automatic screw machines and the like.

The present invention coutemplctes the use oi two induction motors which may be of the squirrel-cage type, and which are mechanically coupled with each other and to the chuck or the like. The two motors may have either t e some or sun ferent synchronous speeds and the some or dii ierent speed-tongue characteristics. The motors are controlled so that they may he operated either cumulatively; that is, generally tending to rotats in the some direction; or differentially, whereby one motor tends to rotate oppositely to the direction of rotation of the other motor. lily also varying the voltage impressed upon one mo tor relatively to the voltage impressed. upon the other motor it is possible to still tcu ther very the combined speed-torque characteristic the motors.

An object of the present invention is to provide an induction motor drive ofiording of the speed-torque characteristic or? the drive within very wide limits.

Another object is to provide e. reversible lnduc= ticn motor rlrive wherein the speed=torcue choir OFFICE "ALTERNATLNG Stensloury, Wan- Hammer, mo,

4W- icelawere Fig. .3 shows a control system which is a modification of the system shown in Fig. 1, and

Fig. 4 graphically illustrates the speed-torque characteristics oi a system embodying the inventicn and comprising two motors having different syncin'ooous speeds and difl'erent inherent speedtorque characteristics.

Referring to Fig. 1 the same illustrates two induction motors M and M which are mechemically coupled with each other. The control apparatus for said motors comprises a main controller or switch A, a selector switch B for the motor M and a controller or switch C for controlling the resistor inserted into the supply circuit for the motor M The controllers A, B and C are shown as of the drum type, but they may be oi any other suitable type. The controller A is provided with stationary drum contact fingers i to 6, inclusive; fingers 5, 3 and i being respectively connected to the lines U, L and l of an alternating current supply system. The fingers ,6, 4 and 2 are respectively connested to the terminals T, T and T of motor M and are also respectively connected to the fingers 25, i3 and 2| of the controller B, which is provided "with stationary contact fingers 2| to 28, inclusive. By rotating the controller A from the neutral position in one direction or the other the lines L L and L are selectively connectable in reverse relationships to the terminals T '1 and 17 and simultaneously in reverse relationships to the fingers 25, 23 and 2!, respectively. The fingers 28, 24, and 22 ct controller B are connected to fingers 31, 34 and 3| of the controller C which is provided with stationary contact ringers St to 39, inclusive. By rotating the controller I-3= in one direction or the other, the fingers 3E. 38 and 31 are reversibly connected to the fingers 2 i, 23 and 25, respectively. Connected between the terminals 3i and 32 is a resistor 1- and'connected between terminals 32 and 33 is a resistor 7 Similar resistors r and 1* and resistors r and r are connected between the fingers as, 35 and 35, 36, and between the fingers ill, 88 and 3d, 39, respectively. The fingers 39, 35 and 5-33 are also connected to the terminals T, T and T of the motor M. The controller (2 is provided with contacts by means of which the resistors 1' to 1' inclusive, are successively short circulted, in the sequence r r r r 1 and r whereby the resistance in the circuit of the motor M and thereby the torque or the motor is varied. The rotors oi the two motors M and M are mechanically coupled as indicated by the com= mon shaft X shown in dotted lines, and shaft x may be rigidly connected to a shaft Y which drives suitable bevel gears which operate the jaws iii, dt', E33 and t6 provided upon the face plate of a lathe chuck it, in any well known or desired manner.

Referring now to Fig. 2 the same illustrates a speed torque curve, marked Motor A or B which represents the individual speed-torque curve of either one of the two motors, it full line voltage is applied thereto. There is also shown the speedasiasse lative.

be operated simultaneously, so that in closing the torques of the two motors M and Ware opposed to each other, whereas in opening they are cumu Other modifications, are obvious or will readily suggest themselves to those skilled in this art.

Referring now to the system shown in Fig. 3, the two motors M and M are again mechanically coupled with each other and with the machine (such as a lathe chuck shown diagrammatically at Z) to be driven thereby. In this case the system comprises a set of controllers A 13- and 0 the controllers B and C being substantially like the respective controllers B and C of the system shown in Fig. l. The controller A, however, is arranged so as to connect the motor M reversibly to the lines L L and L upon operation oi. the controller in opposite directions,

torque curve Bo, which is the same as the first mentioned speed-torque curve, except for reverse rotation of the motor. If a given resistor is inserted into the motor circuit the curve R1 is obtained, whereas if a resistor of greater value is inserted, the speed-torque curve R2 is obtained. The speed-torque curve marked "Motors A and B represents the cumulative or combined values or the speed-torque curves of both motors, if full line voltage is applied thereto.

now the two motors are energized Ior rotation in the same direction with the resistor providing the aforementioned curve R1 inserted into the circuit of the second motor, the speedtoroue curve obtained is indicated by A+R1, whereas ii the resistor providing the aforementioned curve R2 is inserted into the circuit of the second motor the curve A+R2 is obtained. If, however, the'second motor is energized in series with the resistor R1 and connected in circuit so as and to connect the motor M directly to the line cumulatively with the motor M for the opening of the jaws, while if the controller A is moved to the closing position the motor M is connected to the lines in series with the controllers B and C the controller B being capable of reversing the direction of rotation of the motor M relatively to the motor M in the manner aforedescribed, while the controller C may be set forthe desired torque of the motor M by varying the resistance in circuit therewith.

Fig. dis a diagram of a system applicable to the controller elements of either of Figs. 1 or 3,

to tend to rotate in the opposite direction, the

Thus the jaws ill to dd, inclusive, (Fig. 1) may b operated to close or open at any desired speed, and the stalled torque with which the laws clamp the work-piece can be controlled over ayery wide range. This makes it possible to close the jaws at a relatively low speed and keep the stalled torque within limits, so as not to injure or mar the work-piece, whereas the laws can be opened at a relatively high speed to permit a quick release of the work-piece.

In normal operation when using the system of- Fig. l the controller L is set sons to insert the desired value of resistance into the circuit of the motor M thereafter the controller B is set so that the two motors will have either cumulative or opposing torques, and thereupon the controller A is operated to energize both motors to close eration of polyphase induction motors in op= or open the jaws, as may be required. It is of v course possible to interlock the controller l3 with the controller A in such a manner that both will re, tors being mechanically coupled to each other,

wherein the two motors have diflerent speed-= torque characteristics and diiferent synchronous speeds. The curve A1+IB1 shows the efiect of connecting the two motors cumulatively, both without resistance in circuit, for opening movement of the chuck jaws; whereas the curves Az-i-(Br-R) and A1-(B1R) show the efiect of adding and subtracting respectively the torque of motor M to or from that of motor M, the torque of motor M being reduced by the insertion of a given value of resistance between the supply lines and the motor terminals. These curves are mere ly illustrative of agreat variety of such curves obtainable by combining motors having various synchronous speeds and speed-torque character= istics.

We claim: 1. A system for controlling the speed of operation of polyphase induction motors in op posite directions, comprising, in combination. two reversible polyphass induction motors, each having a rotor, said rotors being mechanically coupled to each other, each motor also" having an energizing winding adapted to induce 2. held rotatable in opposite directions selectively, means for connecting said windings in parallel with each other including means for separately de termining the direction of rotation of said fields relatively to each other for different directions of joint operation of said motors, selective means afiordlng joint energization of said windings for operation of said motor in opposite directions of rotation, and means for selectively varying the speed-torque characteristic of at least one of said motors, to thereby vary the combined speed-torque characteristics of said motors upon joint operation thereof in opposite directions, respectively. I

y 2. A system for controlling the speed of op osite directions, comprising, in combination, a source of energy supply, two reversible polyphase induction motors, each having a rotor, said ro= adapted to induce o, o opposite oii'eciziczis selecii oi ioioioz's hav s; section there o co oi tively to each other for difiereni; directions of joint operation of ssid motors, selective moons oifoseiingjoist action of soiei to said source foe opo' siion; oi said motors in 0? posise directions or rotation, and means ooeroiole at will for vezyiog the speeci iorque character of one seiel roicio'rs through relatively wide range upon connection of its energizing Winding to said soui'ce ior sit-emote directions of robotics of said field, to thereby vosy the com 'oineo, soeed icioue olioiecteristics oi soiel moioi's for 301m operation ilieieoi" in opposite directions of rotation, zesgs iivei" v 3. A sysiem oi coni or polyonese induction motors comprising, com? 'soiioo, e energy supply, a flesoreversible poly oiisse incluc tion motor having gives speed-torque chos aoieristio upon connection the of to said souyce in either z'eleiioo, second revelsilcle poly-phase induction mctoo having its iDfiUf, mechanically coupled to the mica said first motes, said second motor normally leaving a, given speed torque chsreoierisiic upon connection to said. sousee in either Kelsi-ion, oncl means ope-r able so will foe varying the speccl torque chm scierisiic of said second motes ilirouglioui, c relatively wide range upon connection thereof is: eiiloei' eels-tics i0 source, to thereby you? the combined spceo i'rcr-o characteristics motors upon joins ooeimloo 'ihei oi in oo oosii-e elii'eoiioss eesoectlveiy, ssid lest oeai means including o voriecie iesisiooce to so ic eludes in or excluded from the primary eii'cuii oi said second. moios,

i. A system for controlling induction motors comprising, in combination, o pole of induction motors escli having a rotor and a primary wind ins, saicl rotors being couples yoeclceoiceliy for joint rotation so fixed speed miles, and selective means for jointly connecting the winc ings of solo motors to s source of energy for alternate rotation in opposite iiiseciioos, iociucl= source iug means for reversing the connections of the windings oi the two motors relsiiveiy so each other and ioic'iioer including means so eileci dif fereni combined speed-tomes chorscieoisiios oi the motors for opposite directions of roteiioo.

ii. A systemic? controlling induction motors comprising, ii'l combination, a pols: of induction motors having elifiereni; iniiesem clzsrocterisiics, eecli motor having" 2 ozimozy winding onci o rotor, said rotors bcingcouoled meclienicslly for joint i'oscilon as fixed speeci ratios, and seieciive for jointly connect in; the primary windings oi motors is s source oi energy for alternate rotation in so ooslie directions, including means ioi' oeversiiis the connections of the windings oi the two mo= tors relatively to escli other euai further i'ociucl rotor, meclmniosl coupling menus for the :coiors oi said moiors providing forgets.- iiontiiereof joio iy st the some speed, means to seversiiiiy connect the primary windings of said motors to a source of energy jointly in a. manner to selectively provide for sctlon of said windings either reversely or cumulatively with i'es oeci to each other, said means including means to effect different combined speed-torque cimmotei-istics of the motors duringxoiction thereof jointly in opposite directions respectively.

1 A sysiem for controlling; induction moiors comprising, in combination, a. pair of induction motors having cliflerent inherent soeed-torque characteristics, means for iii-echsmcslly coupling the sctors of said motors to provide for joint so-tssio's thereof at fixed speed ratios, and means for jointly connecting the primary windings of said motors io s source oi" energy for alternate rotation in opposite slirections selectively, including means so efieci; different speed-torque characteristics for opposite directions of rotation of one of the memes.

8. A system for controlling induction motors comprising, in combination, a pair of polyphase inoluciioo. motors having; different synchronous speecs, motor having a primary winding seal is eoioi', mechanical coupling means for the rotors psovioiins ioi joint rotation at fixed speed ratios thereof, means to reversibly connect the pi imsiy wioeiitoes of said motors to a source of energy jointly, and means to vary the inherent speecl-iorque characteristic of at least one of said motors is effect different combined speed torque characteristics oi the motors in opposite direc izioos of rotation, i

A system for ooisiiolling induction motors comioioeiiou, pair of polyphase iooluciios. motors having: different synchronous speeds, escl'i motor having o primary ridingend so some, mechanics]! couoliog mean for the rotors orovieiing' ior joins rotation atfixed speed ostios thereof, means to jointly connect the primoa'y "windings of said motors to a. source of energy reveisiloly find/o1" reversely relatively to each otliei: and associated means to vary the iniiei'e oi; soeeiitoiuue characteristic of one oi. ssicl motors to e Jeci; clilierent combined speediorqoe cli ciesisizics of the motors upon joint rotation 01 size TOWES thereof in opposite direciions i-esoectlyeiy.

iii. A sysiem for oonirolling" induction motors comprising, in combination, a. pair of polyphase induction motors each having a. primary wind.- ing and a rotor, mechanical coupling means for. the rotors of soici motors providing for Joint rotation at fixed speed ratios thereof, means to yeversibiy connect ilie primary windings of said motors to a source of energy jointly, and means so vary; the speeci -izoroue characteristic of one motor to afford difrerent resultant speed-torque characteristics of said motors for opposite direciions of rotsiioo,

ii. A system for coma-oiling induction motors comprising, in combination, a pair of polyphase induction moioss each having a orimary windins and a rotor, mechanical coupling means for the rotoys oi sold moiors providing for joint rotation as fixed speed ratios thereof, and means o seversilsiy connect the primacy windings of ssici iiioios to s source of enemy jointly, said iosi; mentioned iociuellng means to reverse the connections of one moi/or relatively t the connections of the other of said motors for opposite directions of rotation.

12. A system for controlling induction motors comprising, in combination, a pair of polyphase induction motors each having a primary winding and a rotor, mechanical coupling means for the rotors of said motors providing for joint rotation at fixed speed ratios thereof, means to reversibly connect the primary windings of both motors to a source of energy Jointly, means to adjust the speed-torque characteristic of one of said motors for at least one direction of rotation thereof, and means to reverse the connections of one motor relatively to the connections of the other motor.

13. A system for controlling induction motors comprising, in combination, a pair of polyphase induction motors, a common shaft for rigidly connecting the rotors of said motors with each other, an individual adjustable impedance connectable in series with the primary winding of at least one of said motors, a commutating switch for adjusting said impedance, and a selector switch for connecting the primary windings of said motors jointly to a source of energy, inclusive of alternative values of said impedance.

14. A system for controlling induction motors comprising, in combination, a pair of polyphase induction motors, a common shaft rigidly connecting the rotors of said motors with each other, an adjustable impedance connectable in series with the primary winding of one of said motors, a commutating switch for adjusting said impedance, and a selector switch for simultaneously connecting the primary windings of both motors directly to a source of energy and for alternatively connecting the primary winding of one motor directly and simultaneously connecting the primary winding of the other motor in series with said impedance to said source.

15. A system for controlling polyphase induction motors comprising, in combination, a pair of polyphase induction motors, means for mechanically coupling the rotors of said motors, an adjustable impedance connectable in series with the primary winding of one of said motors, a commutating device for adjusting said impedance, and associated means operable at will to simultaneously connect the primary windings of both motors directly to a source of energy for rotation in one direction, said means being also operable at will to alternatively connect the primary winding of one motor directly to said source and to simultaneously connect the primary winding of the other motor to said source in series with a predetermined portion of said impedance for rotation in the opposite direction.

16. A reversible motor drive comprising, in combination, a pair of polyphase induction motors, means for mechanically coupling the rotors of said motors, a resistance adapted to be included in or excluded from the circuit of the primary winding of one of said motors, means operable at will to adjust the value of said resistanceto be included in said circuit. and associated means operable at will to simultaneously connect the primary windings of both motors to a'suitable source of energy for operation thereof cumulatively to effect rotation of said drive in one direction, said means being also operable at will to alternatively connect the primary windings of said motors to said source in reverse relationship to each other to effect rotation of said drive in the opposite direction. said resistance adjusting means being operable at will to vary the speed-torque characteristic of its associated motor under either of said conditions, for the purpose set forth.

EDWIN W. SEEGER.

CARROLL STANSBURY. 

